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Bureau of Mines Information Circular/1983 




Measuring Noise From a Continuous 
Mining Machine 



By Roy Bartholomae, John Kovac, 
and John Robertson 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8922 



Measuring Noise From a Continuous 
Mining Machine 



By Roy Bartholomae, John Kovac, 
and John Robertson 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



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This publication has been cataloged as follows: 



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Bartholomae, R. C 

Measuring noise from a continuous mining machine. 

(Information circular / United States Dept. of the Interior, Bureau of 
Mines ; 8922) 

Includes bibliographical references. 

Supt. of Docs, no.: I 28.27:8922. 

1. (.oal-mining machinery— Noise— Measurement. I. Kovac, John. 
II. Robertson, John. III. Title. IV. Series: Information circular 
(United States. Bureau of Mines) ; 8922. 



-WmfrAM- [TN813] 622s [622'.028] 82-600370 



CONTENTS 



Page 



Abstract 1 

Introduction 2 

Background 2 

Statement of the problem 2 

Technical approach 3 

Development of synthesized coal seam 4 

Laboratory noise studies in the MNTF 4 

Summary of A-weighted overall sound pressure levels 10 

A-weighted reverberant noise spectra 

Idling noise 

Coal cutting noise 

In-mine noise study 

Comparison of in-mine and laboratory results 

ILLUSTRATIONS 

1 . Noise level time data for underground face equipment 2 

2. Contribution of major sources for continuous mining machine 3 

3. Wyle-USBM LCA before the installation of anechoic enclosure 6 

4. Real and syn-coal samples before and after 1/2-inch (l.,27-cm) depth of cut 

at 64 ips (1.6 m/s) '. 7 

5. Variation of acoustic power with mechanical power for linear cuts of real 

and syn-coal samples 8 

6. Lee-Norse HH105 continuous miner at the MNTF — overall view and closeup of 

cutterhead and syn-coal seam 9 

7. Typical reverberant noise spectra of main hydraulic pumps at idle 12 

8. Reverberant noise spectra of unloaded conveyor noise 12 

9 . Reverberant noise spectra of loaded conveyor 13 

10. Reverberant noise spectra of syn-coal cutting noise 13 

11. Reverberant noise spectra of syn-coal cutting noise with drum heads cov- 

ered with acoustic treatment 14 

12. Schematic of Lee-Norse continuous miner showing measurement locations 14 

13. Comparison of in-mine and laboratory measurements of unloaded conveyor 

noise with tail boom deflected 16 

14. Comparison of in-mine and laboratory measurements of coal cutting noise... 16 

TABLES 

1 . Cutting force variation with coal type 5 

2. Summary of A-weighted overall sound pressure levels measured in the rever- 

berant field 10 

3. Summary of noise data for Lee-Norse 265 continuous miner 15 



MEASURING NOISE FROM A CONTINUOUS MINING MACHINE 

By Roy Bartholomae, ' John Kovac, 2 and John Robertson 3 



ABSTRACT 

Noise generated by continuous mining machines in underground coal 
production is an important health hazard. Bureau of Mines Contract 
J0387229 covers investigation of this noise through laboratory tests of 
simulated cutting operations and through in-mine noise measurements. 
The results of these investigations indicate that coal cutting noise 
and conveyor noise are dominant sources of mining machine operational 
noise. Typical noise levels for both cutting and conveying operations 
are approximately 97 dBA (decibels A-weighted) . For full operation of 
all machine systems, the overall sound pressure level is approximately 
101 dBA. In-mine and laboratory test results show excellent agreement 
in both A-weighted overall levels as well as in A-weighted one-third- 
octave band spectra. 

^ Supervisory electrical engineer, Pittsburgh Research Center, Bureau of Mines, 
Pittsburgh, Pa. 

2 Supervisory mechanical engineer, Pittsburgh Research Center, Bureau of Mines, 
Pittsburgh, Pa. 

^Technical director, Research Engineering, Wyle Laboratories, Huntsville, Ala. 



INTRODUCTION 



BACKGROUND 

In response to the Federal Mining 
Health and Safety Acts of 1969 and 1977, 
which established maximum noise levels 
permissible for mining personnel, the Bu- 
reau of Mines has undertaken a number of 
research programs aimed at reducing the 
noise associated with mining operations. 

One of the more serious noise problems 
in the coal mining industry is associ- 
ated with the operation of continuous 
mining machines in underground coal pro- 
duction. The continuous mining method 
is by far the most common underground 
coal extraction procedure in use today; 
over 2,000 machines are in operation, ac- 
counting for approximately 60 pet of 
the total tonnage of coal mined under- 
ground in the United States. 4 Figure 1 
shows the operating time per shift and 
noise level in the major mode of opera- 
tion for typical underground face equip- 
ment. The continuous mining machine 
ranks second only to the pneumatic s top- 
ing drill as a source of underground 
noise at the face. Because of the sever- 
ity of continuous mining machine noise, 
the present widespread use of this equip- 
ment, and its increasing future appli- 
cation, the Bureau has undertaken a 
comprehensive noise control program for 
continuous mining machines. 

STATEMENT OF THE PROBLEM 

The overall noise levels observed 
around continuous mining machines result 
from the combined contributions of sev- 
eral "independent" noise sources. These 
sources, which are keyed to the various 
operations of the machines, can be di- 
vided into four general categories: Cut- 
terhead, conveyor, drive train, and hy- 
draulic system. 

4 Bobick, T. G., and D. G. Giardino. 
The Noise Environment of the Underground 
Coal Mine. MESA Informational Report 
IR 1034, 1976, 26 pp. 



A noise survey system was conducted on 
a representative sample of continuous 
mining machines, 5 and a summary of the 
results is presented in figure 2. These 
data show that the cutterhead and the 
conveyor are major noise sources in terms 
of their contribution to the overall 
noise level generated by the continuous 
mining machine. The drive train and hy- 
draulic system, on the other hand, are 
secondary noise sources because of their 
smaller contribution to the overall noise 
levels. In addition, drive train and 

5 Madden, R. Abatement of Noise of Con- 
tinuous Mining Machines. Phase II: 
Noise Sources and Control . Bolt Beranek 
& Newman, Inc. report under BuMines Con- 
tract H0 155 113, February 1976, 67 pp.; 
available for consultation at Pittsburgh 
Research Center, Bureau of Mines, Pitts- 
burgh, Pa. 



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AVERAGE OPERATING TIME, min per shift 



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FIGURE 1. - Noise level time data for under- 
ground face equipment. 



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FIGURE 2. - Contribution of major sources for 
continuous mining machine. 



hydraulic system noise is largely depen- 
dent on the design and operating condi- 
tion of the individual machines. 6 

At present, the Bureau has two major 
programs underway to investigate continu- 
ous mining machine noise: (1) contract 
H0155113, "Abatement of Noise of Continu- 
ous Mining Machines," Bolt Beranek & New- 
man, Inc.; (2) contract J0387229, "Inves- 
tigation and Control of Noise Generated 
During Coal Cutting," Wyle Laboratories. 

The emphasis of the first contract is 
the investigation and control of contin- 
uous mining machine conveyor noise; the 
emphasis of the second contract is the 
investigation and control of cutterhead 
noise. The results reported in this pa- 
per were obtained under the latter con- 
tract. Both contracts are largely based 
on the laboratory investigation of con- 
tinuous mining machine noise. Because 
problems of logistics, productivity, and 
permissibility greatly impede research 
and development studies under insitu con- 
ditions , the development of meaningful 
laboratory test methods was a primary ob- 
jective of the present study. The pres- 
ent paper emphasizes (1) the development 
of laboratory apparatus and test methods 
for the investigation of continuous min- 
ing machine noise and (2) evaluation from 
laboratory test results of the noise 
source characteristics. Future studies 
will investigate noise control concepts 
and lead to the development of prototype 
quiet hardware. 



TECHNICAL APPROACH 



Work under contract J0387229 has con- 
tributed significantly to a definition 
and better understanding of the noise 
produced by continuous mining machines , 
with specific emphasis given to coal cut- 
ting noise. The technical approach to 
this study has been based on extensive 
laboratory testing of a Lee-Norse HH105 7 
continuous miner cutting a synthesized 
coal (syn-coal) seam. To facilitate 
accurate interpretation of laboratory re- 
sults, supplementary tests have been con- 
ducted to define the physical and acous- 
tical characteristics of the syn-coal 



seam. Also, the accuracy of laboratory 
simulation has been evaluated by compar- 
ing laboratory noise data with similar 
data taken during the insitu operation of 
a continuous mining machine underground. 

Specific areas of emphasis under the 
present contract have been (1) develop- 
ment of a syn-coal seam to facilitate 

^Work cited in footnote 5. 

'Reference to specific products does 
not imply endorsement by the Bureau of 
Mines. 



laboratory studies of continuous mining 
machine coal cutting noise in the Wyle 
mining noise test facility (MNTF), 
(2) laboratory noise studies of a Lee- 
Norse HH105 continuous miner in the 
MNTF, and (3) in-mine noise studies of a 



Lee-Norse HH265 8 continuous miner. Re- 
sults from each of these areas of study 
are summarized in the following sections. 
In addition, a comparison of in-mine 
and laboratory noise measurements is 
presented. 



DEVELOPMENT OF SYNTHESIZED COAL SEAM 



The work to develop a syn-coal seam 
consisted of preliminary studies using a 
small sample of several recipes to deter- 
mine the most favorable recipe from the 
viewpoint of cutting forces and noise as 
a function of cutting conditions. The 
most favorable recipe was selected on the 
basis of similitude of these parameters 
to those of real coal. For both syn-coal 
and real coal samples, tests were per- 
formed using the Wyle -Bureau linear cut- 
ting apparatus (LCA) located at Wyle's 
Huntsville, Ala., facility (fig. 3). 
This facility provided for measuring the 
three orthogonal components of cutting 
force for a typical pick speed and depth 
of cut . 

Based upon the results from preliminary 
studies of various syn-coal recipes, 
preparations were made for casting a 
large seam of syn-coal in the Wyle 
100,000-ft 3 (2,831-m 3 ) reverberation 
chamber. The recipe used was 42 pet 
stoker-grade coal, 42 pet bottom ash, 
and 16 pet portland cement. As this seam 
was poured, sample blocks were cast for 
each truck load of mixture for later 
calibration using the LCA. A summary of- 



test results for both syn-coal and real 
coal is presented in table 1. These re- 
sults indicate that the Wyle syn-coal 
is harder than real coal, whereas pre- 
liminary tests showed good agreement. 
This discrepancy is explained by the ab- 
sence of air bubbles in the commercially 
mixed samples. Figure 4 shows typical 
coal and syn-coal samples before and af- 
ter cutting. 

Although the Wyle syn-coal is harder, 
the recipe appears to give a good approx- 
imation of real coal on the basis of 
noise measurements as shown in figure 5. 
These results show that the acoustic ef- 
ficiency of noise generation from the 
mechanical power expended to cut coal is 
approximately the same for real coal and 
syn-coal. This fact provides for corre- 
lating laboratory noise studies using 
syn-coal with other tests using real coal 
on the basis of mechanical power expanded 
(i.e., cutting force, F z , times velocity 
of cut, V c ). Further evidence that the 
syn-coal seam provides good acoustic si- 
militude between in-mine and laboratory 
tests is discussed later. 



LABORATORY NOISE STUDIES IN THE MNTF 



Noise studies were performed in the 
MNTF using a Lee-Norse HH105 continuous 
miner. These studies focused on the in- 
vestigation of coal cutting noise for a 
continuous mining machine using a syn- 
coal seam in a surface acoustic test 
facility. Figure 6 shows the miner in 
the MNTF. A number of significant stud- 
ies have been performed and are briefly 
summarized in chronological order, as 
follows: 

Test A . — Tests were performed to record 
"idling" noise for the major continuous 



mining machine subsystems. Included were 
(1) main hydraulic pumps, (2) cutterhead 
rotation with main hydraulic pumps, and 
(3) unloaded conveyor with main hydraulic 
pump. Recorded data consisted of rever- 
berant sound pressure levels. 

8 In-mine noise studies were made of a 
HH265 miner since a HH105 was not readily 
available for study. Future activities 
under this contract may include in-mine 
and laboratory tests of the same miner. 











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FIGURE 3. - Wyle-USBM LCA before the installation of anechoic enclosure. 



PITTSBURGH SEAM COAL 





WYLE SYN - COAL 





FIGURE 4. - Real and syn=coal samples before 
cut at 64 ips (1.6 m/s). 



rl, (') and after (H, P) 1/2-inch (1,27-cm) depth of 



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miner conveyor 
cuttings. 



loaded with syn-coal 



I 2 3 4 5 6 
LOG MECHANICAL POWER, w 

FIGURE 5. - Variation of acoustic power with 
mechanical power for linear cuts of real and 
syn-coal samples. 

Test B . — Sump and shear cuts were made 
in the syn-coal seam to provide for the 
measurement of coal cutting noise. Re- 
corded data consisted of reverberant 
sound pressure levels and coal face ac- 
celeration. These were the first cuts 
into a flat, simulated coal face. Subse- 
quent cuts were into a simulated coal 
face that was concave, corresponding to 
the arc of the miner boom arm and cutting 
head. 

Test C . — Sump and shear cuts were made 
in the syn-coal seam only a partial 
width (26 in [0.66 m] ) of the cutting 
head. The primary purpose of this test 
was to evaluate an instrumented pick 
that had been adapted to the cutting 
head. In addition to pick force data, 
the reverberant acoustic and coal face 
vibration data were collected. 

Test D . — Acoustic data were taken 
for the operation of the continuous 



Test E . — Sump and shear cuts were made 
in the syn-coal seam with the full-width 
cutting head and an instrumented pick. 
For this test, the instrumented pick was 
"floating" on the load cell rather than 
rigidly attached. (Initial tests con- 
ducted of the instrumented pick, test C, 
were for a rigid mount to the load cell.) 
Recorded data included pick force, rever- 
berant sound pressure levels, and coal 
face vibration. 

Test F . — Sump and shear cuts were made 
in the syn-coal seam with the cutting 
drum covered with acoustic treatment. 
This treatment consisted of approximately 
2 in (5 cm) of acoustic foam with an ex- 
terior covering of vinyl. The purpose of 
these tests was to absorb drum head vi- 
brational noise in order to establish 
source-specific contributions to the 
overall coal cutting noise environment. 
Recorded data consisted of pick force and 
reverberant sound pressure levels. Also, 
loaded conveyor noise with the tail boom 
fully deflected (45° to the left) was 
recorded. 

Test G . — Shear cuts in the syn-coal 
seam were made at a depth of approximate- 
ly 18 in (46 cm) to assess the effect of 
deep-cut loading conditions on coal cut- 
ting noise. At this depth of cut, it was 
possible to actually stall the cutting 
head unless careful control of advance 
rate was maintained. Configurations 
consisted of (1) acoustically treated 
drum head and boom arm, (2) acoustically 
treated drum head, and (3) untreated 
baseline machine. Recorded data con- 
sisted of pick force and reverberant 
sound pressure levels. 





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FIGURE 6. - Lee-Norse HH105 continuous miner at the MNTF-overall view (top) and closeup of 
cutterhead and syn-coal seam (bottom). 



10 



SUMMARY OF A-WEIGHTED OVERALL SOUND PRESSURE LEVELS 



A summary of the test results is pre- 
sented in table 2. These data are A- 
weighted overall sound pressure levels 
measured in the reverberant field. The 
reverberant levels appear to give a good 
approximation of levels at the operator 
station when they are compared with mea- 
surements taken underground. Several im- 
portant observations from table 2 should 
be noted: 

1. The predominant sources of noise 
are conveyor operation and coal cutting. 
For normal operation with a loaded con- 
veyor, these two major sources produce 
approximately equal noise levels (93 to 
100 dBA). 

2. Unloaded conveyor operation re- 
sults in the single most severe noise, 



particularly for a deflected tail boom, 
where the "clanking" of conveyor flights 
along the sideboards and tail roller is 
especially influential in producing 
noise. 

3. According to the MNTF coal cutting 
noise studies, the drum cutting head 
could account for up to a 10-dBA increase 
in noise above that due to coal frac- 
turing. This is evident in the 3.5- to 
10.2-dBA noise reduction observed in the 
results for the acoustically treated drum 
head. 

4. Main hydraulic pump noise produces 
only moderate noise levels. A slight re- 
duction in pump noise occurred during 
cutterhead rotation. 



TABLE 2. - Summary of A-weighted overall sound pressure levels measured 
in the reverberant field 



Operating mode 



dBA 



Idling: 

Main hydraulic pumps 83.5- 84.1 

Main pumps plus cutterhead rotation 81.5 

Main pumps plus unloaded conveyor: 

With straight tail boom 98.7 

With tail boom deflected 50 pet 102.7 

With tail boom deflected 100 pet 104.6 

Main pumps plus loaded conveyor: 

With straight tail boom , 93.3 

With tail boom deflected 100 pet 100.3 

Coal cutting — baseline configuration: 

Sump — to 8 in (0 to 20 cm) 94.8 

Shear — approximately 8-in (20-cm) depth 97.0 

Deep shear — approximately 18-in (46-cm) depth 99.6 

Coal cutting — acoustically treated drum: 

Sump— to 8 in (0 to 20 cm) 91.2 

Shear — approximately 8-in (20-cm) depth 92.6 

Deep shear — approximately 18-in (46-cm) depth 89.4 



11 



A-WEIGHTED REVERBERANT NOISE SPECTRA 



IDLING NOISE 

A-weighted one-third-octave-band noise 
spectra taken in the reverberant field of 
the MNTF for the main hydraulic pumps and 
the unloaded conveyor are presented in 
figures 7 and 8, respectively. Discrete 
tones are evident in the pump noise spec- 
tra, with slight variations occurring 
from test to test. The unloaded conveyor 
noise spectra clearly show the increase 
in spectrum levels as the "clanking" in- 
creases with an increase in tail boom 
deflection. 

For the loaded conveyor operation, a 
noise reduction, relative to an unloaded 
conveyor, of approximately 5 dBA results. 
The loaded conveyor noise spectra for 
straight and fully deflected tail booms 
are shown in figure 9. 

COAL CUTTING NOISE 

A-weighted one-third-octave-band spec- 
tra for both sump and shear cutting oper- 
ations are presented in figure 10. Noise 
levels during sumping operations were be- 
low those for shear cutting owing to a 
difficulty in obtaining the same feed 



rate achieved during shear. This limita- 
tion was due to limited miner traction 
and the fact that certain portions of the 
coal face were not fully cut away during 
sumping because of the absence of bits in 
front of the boom arms that support the 
drum cutting head. For the deep-cut 
spectrum in figure 10, the miner cutting 
head was loaded almost to the stall 
point , and these data should represent 
near maximum loading conditions on the 
cutting head for this machine. 

A-weighted one-third-octave-band noise 
spectra for the acoustically treated 
drum are presented in figure 11. Sump 
and shear cut for this configuration 
correspond closely to those conditions 
for the baseline bare-head configuration 
tests. Consequently, a comparison of 
figures 10 and 11 will reveal potential 
noise reduction that could be effected by 
developing a quiet-cutting head. As pre- 
viously noted, this noise reduction could 
range up to 10 dBA; a 5- or 6-dBA reduc- 
tion is probably a realistic goal since, 
in most instances, the drum probably 
would be only moderately loaded, as rep- 
resented by the 8-in (20-cm) depth shear 
cuts. 



IN-MINE NOISE STUDY 



In-mine noise data were recorded during 
the operation of a Lee-Norse model 265 
Hard Head continuous miner in the Pond 
Creek Mine at Rawl, W. Va. The following 
is a summary of the results and analysis 
of this study. 

Noise data were recorded at three loca- 
tions around the miner with the miner 
operating in several different modes to 
facilitate the identification of pre- 
dominant noise sources. The test proce- 
dure consisted of operating the miner 
in idling and coal cutting modes and 



recording the noise for each major sub- 
system (main hydraulic pump, conveyor, 
and cutting head) as the subsystems were 
activated, both independently and in com- 
bination with each other. During these 
tests, measurements were taken (1) at the 
operator's station, (2) near the main 
pump on the opposite side of the miner 
from the operator's position, and 
(3) near the cutterhead. Figure 12 shows 
the general location of the measurements, 
and table 3 summarizes the noise data for 
the Lee-Norse 265 miner. 



12 



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ONE-THIRD-OCTAVE-BAND CENTER FREQUENCIES, Hz 
FIGURE 7. - Typical reverberant noise spectra of main hydraulic pumps at idle. 



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FIGURE 8. - Reverberant noise spectra of unloaded conveyor noise. 



13 



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X^O \B0 XI60 X3I5 X630 XJ250 X2500 X^OOO X^IQOOO X^OpOO 

ONE-THIRD-OCTAVE-BAND CENTER FREQUENCIES, Hz 
FIGURE 9. - Reverberant noise spectra of loaded conveyor. 



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KEY 
18— in depth shear cut 
Sumping in (0 to 8 in) 
8-in depth shear cut 




IE 



J I I I I I I I I I ■ I I I l_l I I 1 I I I I 1 I I L 



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FIGURE 10. - Reverberant noise spectra of syn-coal cutting noise. 



14 



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FIGURE 11. - Reverberant noise spectra of syn~coal cutting noise with drum heads covered with 



acoustic treatment. 




FIGURE 12. - Schematic of Lee-Norse continuous miner showing measurement locations. 



TABLE 3. - Summary of noise data for Lee-Norse 265 continuous miner 



15 



Operating mode 


Sound pressure level, dBA 1 




Position 1 


Position 2 


Position 3 


Idling: 


89.7 
2 88.7 

3 102.3 
97.0 

4 97.0 
5 100.5-101.7 


93.4 
NR 

NR 
NR 

96.3 
97.5-99.7 


88.2 


Main pump plus cutting head.... 
Main pump plus cutting head and 

Loading: Main pump plus conveyor 
Cutting: 


2 85.0- 86.0 

99.4 

NR 

101.0 




102.7 



NR Not recorded. 

See figure 12 for position locations. 

Decrease in pump noise when cutterhead is activated causes a net re- 
duction in total noise. Water spray caused 1-dB increase in noise at 
position 3. 

Note high level of conveyor noise. Clanking of flights on sideboards 
was present. Conveyor was slightly loaded with coal. 

Inferred from other measurements. 

Conveyor clanking caused a 1.2-dB increase in total noise when the 
conveyor tail boom was deflected. 



Results are presented as A-weighted 
overall sound pressure levels for three 
measurement locations and different modes 
of operation. The most relevant data are 
position 1 results, which correspond to 
conditions at the operator's station. 
Measurements at positions 2 and 3 were 
taken to define the near-field character- 
istics of localized noise sources. The 
following noise characteristics were evi- 
dent in the test results: 

1. Predominant sources of noise at the 
operator's position are coal cutting 
noise from the face area and conveyor 
noise associated with the removal of coal 
from the face by the mining machine. 
These two sources of noise have approxi- 
mately equal impact on the operator, each 
producing broadband noise with an overall 
A-weighted level of approximately 97 dBA. 



Overall noise levels experienced by the 
operator during coal extraction are ap- 
proximately 100 dBA for a fully opera- 
tional mining machine. 

2. When the tail boom on the conveyor 
is deflected, the conveyor flights impact 
upon the sideboards, causing a distinct 
"clanking" noise. This "clanking" may 
increase operator noise exposure by 1 to 
2 dBA for a loaded conveyor and up to 
5 dBA for an unloaded conveyor. 

3. The main hydraulic pump produces 
noise characterized by discrete tones in 
the 630- , 1,250-, and 2,000-Hz one- 
third-octave bands. This subsystem oper- 
ating alone exposes the operator to an 
A-weighted overall sound pressure level 
of approximately 90 dBA. 



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FIGURE 13. - Comparison of in-mine and laboratory measurements of unloaded con- 
veyor noise with tail boom deflected. 



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FIGURE 14. - Comparison of in-mine and laboratory measurements of coal cutting noise. 



17 



COMPARISON OF IN-MINE AND LABORATORY RESULTS 



Previous studies 9 of the noise asso- 
ciated with the in-mine operation of a 
Lee-Norse 265 continuous miner revealed 
that the conveying and cutting operations 
produce approximately equal noise levels 
underground. A comparison of measure- 
ments taken in the MNTF with underground 
measurements is presented in figures 13 
and 14. These data compare the in-mine 
one-third-octave-band spectra taken at 

_ _ 

^Robertson, J. E. An In-Mine Survey of 
Noise Generated by a Lee-Norse 265 Hard 
Head Continuous Miner. Wyle Laboratories 
Tech. Memor. TM 79-7 (BuMines contract 
J0387229), August 1979, 32 pp. 



the operator's position with the rever- 
berant field spectra taken in the MNTF. 
Figure 13 presents noise data for un- 
loaded conveyor operation, and the close 
agreement between in-mine and labora- 
tory measurements is evident. Similar 
noise data are present in figure 14 for 
coal cutting with the conveyor off. The 
agreement shown in figure 14 is particu- 
larly significant since the laboratory 
measurements were taken for a continuous 

mining machine cutting a syn-coal seam. 
These results appear to establish the 
feasibility of performing noise control 
studies in the laboratory, as is being 
pursued under the present contract. 



INT.-BU.OF MINES,PGH.,P A. 26691 




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